Immunoassays for early detection of diseases or detection of potential risks are required to have higher sensitivity to detect and measure a minute amount of analyte contained in a sample.
As an example of a method for detecting and measuring a minute amount of analyte contained in a sample with high sensitivity, a measuring method using SPFS (Surface Plasmon-field enhanced Fluorescence Spectroscopy) is known.
FIG. 5 is a schematic structural view for illustrating the structure of a conventional surface plasmon-field enhanced fluorescence spectroscopy apparatus (hereinafter, sometimes referred to as “SPFS apparatus”).
As shown in FIG. 5, a SPFS apparatus 100 comprises a sensor chip mounting part 111, and is configured so that a sensor chip 110 is mounted on this sensor chip mounting part 111.
The sensor chip 110 comprises a dielectric member 112 and a sensor part 116 formed by immobilizing a ligand in a predetermined position on a fine flow channel 118. The fine flow channel 118 is formed on a metal thin film 114 interposed between the fine flow channel 118 and a main surface 112a of the dielectric member 112.
On the dielectric member 112 side of the sensor chip 110 mounted on the sensor chip mounting part 111 of the SPFS apparatus 100, a light source 120 and a light-receiving means 132 are provided. The light source 120 emits excitation light 122 so that the excitation light 122 enters an incidence surface 112i of the dielectric member 112 and the sensor part 116 is irradiated with the excitation light 122 at a predetermined incident angle θA at which attenuated total reflection (ATR) occurs at the metal thin film 114. The light-receiving means 132 receives reflected light 124 that is light emitted from the light source 120 and reflected by the metal thin film 114.
On the other hand, a light-detecting means 130 is provided above the sensor chip 110. The light-detecting means 130 receives fluorescence 134 emitted from a fluorescent material labeling an analyte captured by the ligand immobilized in the sensor part 116.
It is to be noted that a light-collecting member 126 for efficiently collecting the fluorescence 134 and a wavelength-selecting functional member 128 are provided between the sensor chip 110 and the light-detecting means 130. The wavelength-selecting functional member 128 removes light other than the fluorescence 134 to selectively transmit only the fluorescence 134.
Such a SPFS apparatus 100 is used in the following manner.
First, a sample solution containing an analyte is introduced into the sensor part 116 through the fine flow channel 118, and then a fluorescent material for labeling the analyte is introduced through the fine flow channel 118 in the same manner to achieve a state where the analyte labeled with the fluorescent material is captured in the sensor part 116.
Then, in such a state, the light source 120 emits the excitation light 122 so that the excitation light 122 passes through the dielectric member 112 and the sensor part 116 is irradiated with the excitation light 122 at a predetermined incident angle θA at which attenuated total reflection occurs at the metal thin film 114. As a result, electric field enhanced by resonance between evanescent waves and surface plasmon from the metal thin film 114 is generated so that the fluorescence 134 from the fluorescent material captured in the sensor part 116 is efficiently excited.
Then, the excited fluorescence 134 is detected by the light-detecting means 130 to detect and measure a minute amount and/or very low concentration of the analyte.
Such an immunoassay apparatus is often used to measure a disease marker contained in the body fluid of a patient, such as blood, urine, or saliva. In this case, not a single marker but two or more related markers are generally measured to diagnose the disease state of the patient from the overall results of the measurements.
Therefore, Patent Literature 1 or 2 discloses that two or more markers are measured at the same time using one device, such as a flow cell or a sensor chip, by providing two or more sensor parts (assay regions) in the one device.